The present invention relates to article carriers and particularly to article carriers suitable for holding a group of metal cans and to the polymer composition from which the articles are formed.
In the past, a wide variety of carriers have been used to contain metal cans in six packs and other arrangements. Usually six packs of beer and soft drinks are packaged in paper wraparound carriers or in band-type unitary flexible plastic web carriers. Such plastic carriers are typically fabricated from low density polyethylene resin cut from a continuous plastic extruded sheet. The carriers have a unitary web main structure which has a plurality of can supporting and engaging loops or so-called aperture portions.
Usually the cans are grouped in a six pack arrangement and subsequently, the plastic carrier is stretched, placed over the cans and released so the stretched loops contract and securely engage the cans. If the loop portions do not engage the cans firmly enough, the heavy filled cans may release from the package. Even if the loop portions are properly tensioned after installation when the cans are rotated within the carrier during production, shipping, display in the retail outlet and during use, the plastic of the loops is subject to failure. The failure occurs usually by (a) the metal of the can sidewall adhering strongly to the plastic of the carrier by spontaneous adhesion and as the can rotates completely tearing the plastic loop, thereby releasing the can from the package, or (b) the metal sidewall of the can adheres to the plastic of the loop upon rotation of the can for long enough to stretch the plastic out of its normal shape, known as necking down of the plastic, and thus opens the can engaging loop to the point where the can may fall from the package.
Both of these failure modes, complete breakage of the loop or extensive stretching causing release, have caused a severe problem in the market place since premature release of the cans from the carrier is a commercially unacceptable situation. The problem is particularly severe when cans are oriented during display to allow for maximum presentation of the product identifying label or so-called billboard. When the sales staff in the store rotates the cans on the shelf to give maximum billboard the carriers are frequently torn or stretched to the point of can release and thus cause a significant amount of product return to the canner.
The problem is worsened when cans are overfilled and water, beer or soft drinks containing sugar contacts the cans and carrier. The sticky fluids dry under hot temperatures during shipping and storage causing the metal cans to adhere even more strongly to the plastic. This makes carrier damage even more probable during can rotation.
One approach to solving this problem has been to use a chilled matte or so-called roughened surfaced chrome roller to emboss surface irregularities onto the carriers after hot melt extrusion of the sheet which will form the carrier blanks. This lessens the actual surface-to-surface contact between the metal can wall and the plastic surface of the carrier. This lessens the adhesion and thus the probability of carrier damage and the corresponding premature release of heavy filled cans from the carrier. However, adding an embossing roller not only adds an expensive extra production step but has been found to slow production since the hot newly extruded sheet which will form the carrier blanks material tends to stick to the chilled roller excessively and significantly lower production line speeds.
Also, since some can styles do not utilize the matte finish carriers, many producers must have two inventories of carriers, one embossed and one plain. This is uneconomical from an inventory control standpoint.
Another approach to solve the problem of carrier damage has been to intimately blend low density polyethylene resin with relatively large amounts of erucamide and with an antiblocking agent like finely divided silica. This composition, while including an antiblocking agent and the long chain fatty acid amide namely erucamide for lubricity, has experienced problems in that after the composition is blended and extruded into sheetstock from which carriers are formed, a long storage time is necessary before the carriers can be die cut. The polyethylene-erucamide material has been found to stick to forming equipment if the extruded film is die cut within about a 24 hour period post extrusion. This is a significant disadvantage causing expense in delayed use during storage awaiting the proper aging of the composition.
Another approach to solve the problem has been to intimately blend low density polyethylene resin with relatively large amounts of oleamide, another long chain fatty acid amide. This composition using oleamide alone not only does not solve the carrier-can sticking problem, it has caused significant amounts of wax build-up on presses, feed rollers and applicating equipment.
Accordingly, there exists a need in the art for a composition of matter which can be formed into carriers, installed with conventional equipment and accept a variety of can designs and surface finishes and resist carrier degradation during can rotating or so-called can facing. The composition should also be useful for forming carriers without equipment fouling immediately after hot melt extrusion into sheetstock.